An example of how the continuing evolution of the web is helping the music world is Pandora. Pandora calls itself a “music discovery service”. It is based on the Music Genome Project, an endeavor that seeks to categorize all musical selections with 400 separate attributes. All music (I mean literally all types of music–this project is huge and is growing every day) is organized by style, tempo, time signature, key signature, instrumentation, dynamic spectrum, etc.
Pandora takes this raw data and makes personalized radio stations for its listeners. You tell Pandora a few songs you like and it uses the attributes of these songs to determine that other music you would like. There is a recommendation engine, so as you are listening you can give particular songs a thumbs up or thumbs down.
Check it out–it is free and really amazing.